Re: what is the regular expression that matches nothing? -- I think it is the null expression. When I do "egrep '' somefile" the result is the same as when I do "cat somefile". The result of "egrep -v '' somefile" is, as expected, nothing. HTH

[Randy Yates]

Stan Brown <the_stan_brown@fastmail.fm> writes:

> There is no regular expression that matches nothing.
>
> I you want to match a zero-length line, use
>       ^$
>
> But the idea of matching nothing has an inherent contradiction. 

I don't see that. Can you explain why you say this?

> Why don't you tell us what you're actually trying to accomplish?

Sure, Stan. I'm trying to setup the EFS package in XEmacs to use a
gateway for FTP. In this mode, EFS requires a regular expression to
identify which machines are accessible without having to go through
the gateway. In my case (this is at work where we have a firewall)
that would be "no machine," i.e., all machines I FTP to (with XEmacs)
will be outside the firewall.  Thus the regexp has to match "nothing."
-- 
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